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Thread: Old 87MM, new owner, starts and runs but dies at idle

  1. #1

    Array
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    03-09-2015
    Posts
    7
    Location

    Lacomb, Oregon
    Vehicle

    1987 Mitsubishi Mighty Max
    Engine

    G54B

    Question Old 87MM, new owner, starts and runs but dies at idle

    Hi all,

    I picked up our '87 MM 2.6 sport from a friend who had relegated it to farm duty the past 5 years. My son and I are using it as vehicle maintenance and manual transmission training. It has the stock carburetor and all the lovely smog hardware still intact. About 118K miles on the odo.

    It currently will start and run with your foot on the throttle but dies when you lift off. It didn't do this initially. It started doing this last Friday after running some errands in town. Ran fine and idled fine til around time they were leaving for home, then it died at each light and whenever the he took his foot off the throttle.

    Knowing it had been a while since it had a tune up, I decided to use this for training with my son. We replaced:

    1. Distributor cap and rotor
    2. PCV valve
    3. Fuel filter
    4. Spark plugs


    ...with no improvement on the idle issue.

    We inspected the vacuum lines for cracks or if any had popped off their connections. All looks normal.

    My next step is to see if the idle speed adjust will address the symptom, but this doesn't feel right. Why would the idle speed suddenly drop?

    I took some spray carb cleaner and degunked the choke plate and interior of the carb while running. Looks better, but again, no improvement.

    Other items of note:

    exhaust is white and coolant level seems to drop with no signs of leakage - suspect head gasket or head crack.

    fuel dribbling into carb when off?

    I suspect that something in the carb is malfunctioning. I don't relish rebuilding the POS carb and would rather do a Weber install but that will have to wait. So any ideas in the meantime for restoring idle would be appreciated.

    thanks,

    Mike

  2. #2

    Array
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    Join Date
    03-09-2015
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    7
    Location

    Lacomb, Oregon
    Vehicle

    1987 Mitsubishi Mighty Max
    Engine

    G54B

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ID:	13662Text in red says "fuel was dribbling from here"

  3. #3

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    08-26-2015
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    2
    Location

    Minneapolis, mn
    Vehicle

    1987 Mitsubishi Mighty Max
    Engine

    G54B
    Hey mikehd, Did you ever figure out what the problem was? I'm having the same issue of starting and running with my foot on the pedal then dying when I take it off. Any info would be helpful. Thanks sportymax.

  4. #4

    Array
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    03-09-2015
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    7
    Location

    Lacomb, Oregon
    Vehicle

    1987 Mitsubishi Mighty Max
    Engine

    G54B
    It cleared up on its own. I noticed that the fuel dribbling noted in the post above yours was gone as well. I think that I may have stirred up crud during the fuel filter replacement (now that's a PITA) which got to the carb and messed up the flow. It must have blown through. I haven't had an idle problem since.

  5. #5

    Array
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    Join Date
    08-26-2015
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    2
    Location

    Minneapolis, mn
    Vehicle

    1987 Mitsubishi Mighty Max
    Engine

    G54B
    Good to know. Thanks.

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